Valve metals such as titanium, zirconium, tantalum and niobium exhibit film-forming properties which provide high corrosion resistance for use in anodes for electrolytic processes.
Dimensionally stable anodes with a titanium base and an electrocatalytic coating comprising a platinum group catalyst are widely used throughout the world for the electrolysis of brines. However, such anodes are subject to more or less rapid passivation in the presence of anodically evolved oxygen, thereby restricting their usefulness for anodic reactions involving the release of oxygen, e.g. as anodes for metal electrowinning processes.
The cost of titanium grids or sheets suitable as an electrode support also restricts their widespread use for operation at relatively low anodic current densities, e.g. in metal electrowinning.
Valve metal powders and more particularly titanium sponge are considerably cheaper than sheet or mesh and are of potential interest as a relatively inexpensive, stable, electrode material, or as a support material for catalysts in general.
Particulate valve metals such as titanium powder or sponge moreover provide a large surface for catalytic reactions, but do not, as such, exhibit adequate catalytic properties, and hence should be combined with catalysts suitable for carrying out desired reactions under industrially acceptable conditions.
Platinum group catalysts provide excellent catalytic properties for various processes but their high cost can at best be justified if they are employed efficiently in as small amounts as possible.
The economical use of platinum group catalysts to activate titanium powder or sponge, or other valve metals in the form of particles, would thus be of considerable interest to provide stable, relatively inexpensive catalytic materials suitable for various purposes, and more particularly for catalytic electrodes.